Generation of Terahertz Radiation by Optical Rectification Using Femtosecond Bessel Beam

Optical rectification is one of the most widely used methods to generate broadband terahertz (THz) radiation using femtosecond laser pulses. In this work, we report the generation of THz radiation from GaP crystals based on optical rectification using a pulsed Bessel beam, i.e., a beam with a spatial profile described by a zeroth-order Bessel function of the first kind. It is shown that the nondiffracting feature of the central spot of the Bessel beam allowed an enhancement of the THz radiation generation efficiency. Compared with a Gaussian beam having the same beam size and pump power as its central spot, the Bessel beam enabled an average increase of the THz radiation power by factors of 1.37, 2.12, and 2.06 from GaP crystals of 1, 3, and 5 mm, respectively. Measurements showed that the spatial profile of the THz radiation followed a Gaussian distribution for both pump beams and increased linearly after the emitters.